python字符串操作

#首字母大写
str = "my name is zhangsan"
print(str.capitalize())
>>My name is zhangsan

#统计字符串里有几个字符
str = 'my name is zhangsan'
print(str.count('i')) #print(str.count('a',5,18))
>>1

#居中，不足按参数形式补全
str = 'my name is zhangsan'
print(str.center(50,'-'))
>>---------------my name is zhangsan----------------

#左对齐，右边不足按参数形式补全
str = "my name is zhangsan, and age is 22"
print (str.ljust(50,'-'))
>>my name is zhangsan, and age is 22----------------

#右对齐，左边不足按参数形式补全
str = "my name is zhangsan, and age is 22"
print (str.rjust(50,'-'))
>>----------------my name is zhangsan, and age is 22

#制表符转换为空格，参数为空格数量
str = 'my name is zh\tangsan'
print(str)
print(str.expandtabs(10))

#判断是否为相应字符结尾
str = 'my name is zhangsan'
print(str.endswith('san'))

#string转换为bytes
str = '我爱中国'
print(str.encode())
>>b'\xe6\x88\x91\xe7\x88\xb1\xe4\xb8\xad\xe5\x9b\xbd'

#bytes转换为string
bs = b'\xe6\x88\x91\xe7\x88\xb1\xe4\xb8\xad\xe5\x9b\xbd'
print(bs.decode())
>>我爱中国

#在规定位置查找字符，找到返回index，找不到-1
str = 'my name is zhangsan'
print(str.find('a',3,10))

#格式化字符串
str = 'my {} is {}'
print(str.format('name','zhangsan'))
>>my name is zhangsan
#可以不按顺序
str = 'my {1} is {0}'
print(str.format('name','zhangsan'))
>>my zhangsan is name
#也可以这样
str = 'my {a} is {b}'
print(str.format(b='name',a='zhangsan!!!'))
>>my zhangsan!!! is name

#用map方式格式化
str = "my name is {name}, and age is {age}"
print(str.format_map({'name':'zhangsan','age':'22'}))
>>my name is zhangsan, and age is 22

#判断是否全大写
str = 'AAA'
print(str.isupper())
>>True

#判断首字母大写
str = 'Aa'
print(str.istitle())
>>True

#判断是不是空格
str = ' '
print(str.isspace())
>>True

#判断是不是由数字字符组成的字符串
str = '111'
print(str.isnumeric())
>>True

#判断是否全字母组成
str = 'aaaa'
print(str.isalpha())
>>True

#检测指定str是否存在与原str中，可以指定开始结束，与find()区别在于，如果没查到会报异常
str = "my name is zhangsan, and age is 22"
print(str.index('a'))
>>4
print(str.index('x'))
>>ValueError: substring not found

#判断是否小写字母组成
str = 'aaa'
print(str.islower())
>>True

#判断是否字母和数字组成
str = 'a12Aaa'
print(str.isalnum())
>>True

#判断是否只由数字构成
str = '111'
print(str.isdigit())
>>True

#用于将序列中的元素以指定的字符连接生成一个新的字符串
str = "-";
seq = ("a", "b", "c"); # 字符串序列
print str.join( seq );
>>a-b-c

#转换字符串中所有大写字符为小写。
str = "my nAme is zhANGSAN, and age is 22"
print (str.lower())
>>my name is zhangsan, and age is 22

#移除字符串头尾指定的字符（默认为空格）
str = "*****this is string example....wow!!!*****"
print (str.strip( '*' ))
>>this is string example....wow!!!

#截掉字符串左边的空格或指定字符，默认为空格
str = "1111my name is zhangsan, and age is 221111"
print (str.lstrip('1'))
>>my name is zhangsan, and age is 221111

#截掉字符串右边的空格或指定字符，默认为空格
str = "1111my name is zhangsan, and age is 221111"
print (str.rstrip('1'))
>>1111my name is zhangsan, and age is 22

#intab替换为outtab，一一对应，转换为ASCII码格式，translate()把ASCII码转换为对于字符
intab = "aeiou"
outtab = "12345"
trantab = str.maketrans(intab, outtab)
print(trantab)
str = "this is string example....wow!!!"
print (str.translate(trantab))
>>{97: 49, 101: 50, 105: 51, 111: 52, 117: 53}
>>th3s 3s str3ng 2x1mpl2....w4w!!!

#返回一个3元的元组，第一个为分隔符左边的子串，第二个为分隔符本身，第三个为分隔符右边的子串。
str = "http://www.w3cschool.cc/"
print(str.partition('//'))
>>('http:', '//', 'www.w3cschool.cc/')

#返回子字符串 str 在字符串中最后出现的位置，如果没有匹配的字符串会报异常，你可以指定可选参数[beg:end]设置查找的区间
str = "1111my name is zhangsan, and age is 221111"
print (str.rindex('isx'))
>>ValueError: substring not found

#返回字符串最后一次出现的位置，如果没有匹配项则返回-1
str = "1111my name is zhangsan, and age is 221111"
print (str.rfind('isx'))
>>-1

#方法把字符串中的 old（旧字符串） 替换成 new(新字符串)，如果指定第三个参数max，则替换不超过 max 次
str = "this is string example....wow!!! this is really string"
print (str.replace("is", "was"))
print (str.replace("is", "was", 3))
>>thwas was string example....wow!!! thwas was really string
>>thwas was string example....wow!!! thwas is really string

#把字符串切割成列表，默认空格为切割符
str = "       1111my name is zhangsan, and age is 221111   "
print (str.split())
>>['1111my', 'name', 'is', 'zhangsan,', 'and', 'age', 'is', '221111']

#按照行('\r', '\r\n', \n')分隔，返回一个包含各行作为元素的列表，如果参数 keepends 为 False，不包含换行符，如果为 True，则保留换行符。
str1 = 'ab c\n\nde fg\rkl\r\n'
print(str1.splitlines())
str2 = 'ab c\n\nde fg\rkl\r\n'
print(str2.splitlines(True))

#用于检查字符串是否是以指定子字符串开头，如果是则返回 True，否则返回 False。如果参数 beg 和 end 指定值，则在指定范围内检查。
str = "this is string example....wow!!!"
print (str.startswith( 'this' ))
print (str.startswith( 'string', 8 ))
print (str.startswith( 'this', 2, 4 ))
>>True
>>True
>>False

#转换成大写
str = "this is string example....wow!!!"
print (str.swapcase())
>>THIS IS STRING EXAMPLE....WOW!!!

#将字符串中的小写字母转为大写字母。
str = "this is string example....wow!!!"
print (str.upper())
>>THIS IS STRING EXAMPLE....WOW!!!

#首字母大写
str = "this is string example....wow!!!"
print (str.title())
>>This Is String Example....Wow!!!

#左边补零
str = "123456789"
print (str.zfill(9))
print (str.zfill(10))
print (str.zfill(11))
>>123456789
>>0123456789
>>00123456789